The present invention relates generally to photovoltaic materials and manufacturing method. More particularly, the present invention provides a method and apparatus for thin film thermal treatment. Embodiments of the invention include a method and apparatus for holding a plurality of extra large substrates for achieving substantially uniform substrate temperature during a thermal process to form a photovoltaic absorber material, but it would be recognized that the invention may be applied for other thin-film treatment applications.
From the beginning of time, mankind has been challenged to find ways of harnessing energy. Energy comes in forms such as petrochemical, hydroelectric, nuclear, wind, biomass, solar, and more primitive forms such as wood and coal. More recently, environmentally clean and renewable source energy has been desired. Clean and renewable sources of energy also include wind, waves, biomass, and the like. Still other types of clean energy include solar energy.
Solar energy technology generally converts electromagnetic radiation from the sun to other forms of energy. These other forms of energy include thermal energy and electrical power. For electrical power applications, solar cells are often used. Although solar energy is environmentally clean and has been successful to a point, many limitations remain before it becomes widely used throughout the world. As an example, one type of solar cell uses crystalline materials, which are derived from semiconductor material ingots. These crystalline materials can be used to fabricate optoelectronic devices that include photovoltaic and photodiode devices that convert electromagnetic radiation to electrical power. However, crystalline materials are often costly and difficult to make on a large scale. Additionally, devices made from such crystalline materials often have low energy conversion efficiencies. Other types of solar cells use “thin film” technology to form a thin film of photosensitive material to be used to convert electromagnetic radiation into electrical power. Similar limitations exist with the use of thin film technology in making solar cells. That is, efficiencies are often poor. Additionally, film reliability is often poor and cannot be used for extensive periods of time in conventional environmental applications. Often, thin films are difficult to mechanically integrate with each other. These and other limitations of these conventional technologies can be found throughout the present specification and more particularly below.
As an effort to improve thin film solar cell technology, processes of manufacturing an advanced CIS and/or CIGS based photovoltaic film stack on sized substrates with planar, tubular, cylindrical, circular or other shapes have been introduced. There are various manufacturing challenges in forming the photovoltaic film stack, such as maintaining structure integrity of substrate materials, controlling chemical compositions of the ingredients in one or more precursor layers, carrying out proper reactive thermal treatment of the one or more precursor layers within a desired gaseous environment, ensuring uniformity and granularity of the thin film material during reactive thermal treatment, etc. Especially, when manufacturing the thin film based solar cell on large sized substrate, temperature uniformity across whole substrate surface is desired. While conventional techniques in the past have addressed some of these issues, they are often inadequate in various situations. Therefore, it is desirable to have improved system and method for processing thin film photovoltaic devices on planar or non-planar shaped, fixed or flexible substrates.